This invention relates to a capacity control system for a variable capacity refrigerant compressor, including an electrically operated capacity control valve having one or more integral sensors for measuring at least the discharge pressure of the refrigerant.
Variable capacity refrigerant compressors have been utilized in automotive air conditioning systems, with the compressor capacity being controlled by an electrically-operated control valve. In a typical implementation, the compressor includes one or more pistons coupled to a tiltable wobble plate or swash plate, and the control valve adjusts the pressure in a crankcase of the compressor to control the compressor capacity. In one common arrangement, for example, a linear or pulse-width-modulated solenoid coil is operated to linearly position (by dithering, for example) an armature of a four-port valve that alternately couples the crankcase of the compressor to the compressor discharge (outlet) and suction (inlet) passages. When the discharge passage is coupled to the crankcase, the crankcase pressure is increased to decrease the compressor capacity; when the suction passage is coupled to the crankcase, the crankcase pressure is decreased to increase the compressor capacity. One example of such a valve is shown in the U.S. Pat. No. 6,116,269 to Maxon, issued on Sep. 12, 2000.
Since an electrically-operated control of compressor capacity is typically based on the operating status of the system, sensors are required to measure the refrigerant temperature or pressure at various locations. For example, both the high-side or discharge pressure and the low-side or suction pressure are frequently measured for control purposes and for detecting abnormal operation of the system. The usual approach is to mount a pressure sensor on a suitable refrigerant conduit, but variability in the position and orientation of the sensor results in variations of the sensed pressure due to transport delay and/or pooling of the refrigerant. Consistent results can only be ensured if the sensors are integrated into the compressor or control valve. For example, the four-port valve shown in the above-mentioned U.S. Pat. No. 6,116,269 includes an integral pressure sensor for measuring the suction pressure of the compressor.
While the above-described approach can be used effectively to control compressor capacity, the cost of the control valve can be relatively high since an external discharge pressure sensor is still required, and a four-port control valve is relatively expensive to manufacture. Accordingly, what is needed is an electrically-operated control valve that is less expensive to manufacture, and that also includes an integral sensor for measuring the discharge pressure of the compressor.
The present invention is directed to an improved capacity control system for a variable capacity refrigerant compressor including an internal bleed passage coupling a crankcase chamber of the compressor to a suction port, an electrically-operated two-port control valve that selectively opens and closes a passage between the crankcase chamber and a discharge chamber, a suction pressure sensor within the control valve for measuring the compressor suction pressure and a discharge pressure sensor within the control valve that is continuously coupled to the discharge chamber for measuring the compressor discharge pressure. A plunger of the control valve is disposed within the passage coupling the crankcase chamber and the discharge chamber, and a solenoid armature linearly positions the plunger within the passage to open and close the passage. The plunger has an axial bore that forms a continuous passage between the discharge chamber and a cavity in which the discharge pressure sensor is retained so that the sensor is continuously exposed to the discharge pressure regardless of the plunger position. The solenoid armature includes a movable coil that interacts with a stationary pole piece including one or more permanent magnets, and balance guides formed on the plunger minimize the magnetic force required to move the plunger.